I have a question about the dimensions. Could you tell me what is the exact measure when fully assembled with nrf24 and with / without goldpins? I have tiny, transparent boxes and curious if I can fit them inside

@NeverDie
None. The plan was to enhance it, so I copied my version 1 to version 2. But then I decided to publish it in Openhardware anyway.
This board is a proof of concept for me.
My next version will have a 8Mhz crystal. The addional powerconsumption is negligable bit the accuracy of timing is much better (and constant, even with dropping voltage).
So the board on OSH Park is identical to the one on Openhardware.io

@GertSanders OK, the issue is in pins_arduino.h in 32PinBoard folder. The standard file is just not good. I'll have to find the right one for tqfp chip.

EDIT: copied the "eightanaloginputs" variant in the variant folder, but still can only upload the first sketch after the bootloader, all other uploads are giving me "avrdude: stk500_getsync() attempt x of 10: not in sync:"

@GertSanders Many thanks for your help. This is probably my bad luck, but I have mixed up C1 and R1 mounting them vertically (not horizontally). What a stupid mistake really given that I have checked it a few times. Anyway, now everything is working.

FYG, I looked at your pins_arduino.h - this is a standard one and it is not correct. I corrected the following entries:

@alexsh1
Double plus good !
As I have no signing capability on my raspberry-turned-gateway I'm glad the hard work to simplify signing was done so well by @tbowmo and @Anticimex. Even without testing it I could assume it would work.

@Anticimex
Well that sounds simple, but I'm more a hardware contributer, this is beyond my capabilities :-), especially in unix arena. I manage software developers for a living, so I know how much I do not know.

Thank you for the update,
Last part what I am missing is battery holder. I was trying to search it in many stores located in my country however I was not able to get it. Is there any internet shop when I can buy online? I have one workaround to soldier different CR battery holder and connect via wires.

@alexsh1 do you plan to use this so small coincell with rfm69? very curious to see results regarding internal res during RX-Tx times...1.8V brownout should not be far i think..or maybe not because the voltage won't stay at 3v but to counter effect, a nice capa at input with a current limiting resistor could help. reading/waiting voltage stabilize before transmitting can help too (I'm doing this with some CR2032 based nodes)

@scalz Yes, that's the plan, but I think I'll come across many difficulties. For now I have the nrf24l01+ version fully working. And started scratching the surface with RFM69. This is nrf24l01+ SMD version and swapping it for RFM69 is not going to be easy. So far I have not seen any adapters for the SMD version.

I'm considering to build a few nodes with this design, could anyone that have done and tested these give some feedback on how it work? Battery life etc. In my case I will mostly use it as window/door sensor and water leakage sensor so it would not send data to frequently.

@GertSanders,
Thank you for the nice, small design. I'm trying to build one myself, but I'm running into issues burning the bootloader using the ArduinoISP sketch on an Arduino Nano (328). Looking at the schematics, the pins of the ICSP header (from left to right, if the headers are facing you) are:
Reset => Pin 10 of Nano
SCK => Pin 13 of Nano
MISO => Pin 12 of Nano
MOSI => Pin 11
VCC => VCC on Nano
GND => Gnd on Nano

I set the board to Arduino Pro or Pro Mini in the Arduino IDE, selected Arduino as ISP and tried to burn the bootloader, but there always is the error message:

avrdude: Expected signature for ATmega328P is 1E 95 0F
Double check chip, or use -F to override this check.
Error while burning bootloader.

Any idea what's wrong?

I built two copies of the board, and I get the same message with both. (mirroring the connectors of the ICSP header doesn't work, either).

@reinhold
Hi, the first thing I would check is to see if you can burn a boot loader on a standard 328P DIP format with the Nano. I'm not sure the ISP sketch, when running on a Nano matches the exact physical pins for MISO, MOSI and SCK. So check that.
I also burnt the boot loader with the sketch, but on a classic Arduino UNO as ISP. Never tried to do this from a Nano as ISP.

@reinhold
Something else I was thinking about. I did burn the boo loader before I mounted a NRF24L01+ board on my stamp size board.
I made another board recently and found that burning a boot loader while the radio is connected, gives me issues like the one you mention: sometimes an unexpected signature error, sometimes it starts and stop loading midway ... That was on a different board, but with basically the same connections between processor and radio.
So I think that you do need to load the boot loader before mounting the radio on the board. As for my newer board where I first found this issue, it was a robot control board I now need to redesign so that I can refresh the boot loader (ro anything else via ISP) with a mounted radio, by providing a "switch" of some kind to isolate the radio when I do not want it to interfere with the ISP loading.

@henninne sorry for a late reply. The battery life is excellent. I have one node working as a door sensor and another one I'm testing as a battery voltage sensor - just sends voltage every 60 mins. The door sensor is powered by two AAA batteries and has been working for 5-6 months and still shows 3.1V+
The battery sensor is running on a coin cell and consumes around 6uA while sleeping.

@GertSanders Thanks for the response.
I had already used the nano to install the bootloader on the linbus analyzer and linbus injector boards, so apparently the nano can be used with the ArduinoISP sketch. I also tried re-installing a bootloader to another nano via the ICSP pins and it worked.

I also tried building my last PCB for your stamp-sized nodes without the wireless module installed, but I get the exact same behaviour. (You are right, it's not so far-fetched that the radio module might interfere with the bootloader installation, since the ICSP header also just breaks out the SPI headers. On the other hand, the slave select for the nrf24l01+ is not pulled low by the arduinoISP, so it should not interfere on the SPI bus...).

@alexsh1
I already tripple checked my wiring (even tried switching MISO/MOSI), but I can't find any problem. In fact, only with this very wiring do I get the "Expected signature for ATmega328P is 1E 95 0F" error message, as only with this wiring, the signature is different from 0x000000. Here's the verbose log of the bootloader burning:

Strangely, I do not get the same signature when I try to burn the bootloader again (0x040404 => 0x0e0808 => 0x080808; 0x820202 => 0xc10101 => 0x820202).
So it seems that communication is somehow possible, but only garbage is observed.

FWIW, I'm using the "Arduino Pro or Pro Mini" (like I did with the linbus boards) with processor ATmega328P (3.3V, 8MHz).

The only difference I can see between the working linbus and nano boards and this stamp-sized node is that the linbus boards have an external crystal, while this stamp-sized node appears to use the internal crystal of the chip. Can this be the difference?

The bootloader burning issue was indeed a problem with the crystal: It seems that the atmega328p that I bought on aliexpress came with the fuse set to external crystal, so they worked fine on all boards with an external crystal, but this stamp-sized node didn't react because the internal oscillator was disabled in the chip. I had some 16MHz SMD crystal lying around, soldered jumper wires to them and manually held them to pins 7 & 8 of the atmega328p while trying to burn the bootloader. That's quite delicate as the pins are so small, but it works astonishingly well.
As boards I used the "MiniCore atmega328" board that allowed me to select the internal crystal and also lower the black-out voltage.

With the external crystal held to the atmega's pins, I was able to properly burn the bootloader and activate the internal oscillator. Now, the board seems to work just fine.
The only issue is that I just realized I don't have any CR1632 batteries. I suppose CR1620 will also work, but that a shorter battery life?